Hydrogen and the structure of transition aluminas
{alpha}-Alumina results from the complete dehydration of several minerals of the form Al{sub 2}O{sub 3}{center{underscore}dot}nH{sub 2}O. The ``transition'' aluminas, {gamma}-alumina, {eta}-alumina, and {delta}-alumina are known to have a spinel structure but the possibility that they contain hydrogen (H) has been the subject of debate. The authors present a series of density-functional theory calculations which, together with available experimental data, show that the spinel aluminas exist over a range of hydrogen content captured by the empirical formula H{sub 3m}Al{sub 2{minus}m}O{sub 3}, with a different greek-letter phases corresponding to different distributions of the Aluminum (Al) ions on the two cation sublattices. Calculations of densities and vibrational frequencies of bulk OH bonds are in excellent agreement with available data. The theory reconciles seemingly inconsistent data and reveals a remarkable property of the spinel aluminas: They are ``reactive sponges'' in that they can store and release water in a reactive way. This chemical activity offers a basis for understanding long-standing puzzles in the behavior of aluminas in catalytic systems.
- Research Organization:
- Oak Ridge National Laboratory, TN (US)
- Sponsoring Organization:
- USDOE; National Science Foundation (NSF)
- DOE Contract Number:
- AC05-96OR22464
- OSTI ID:
- 20000132
- Journal Information:
- Journal of the American Chemical Society, Vol. 121, Issue 33; Other Information: PBD: 25 Aug 1999; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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